Feature: Toggle the table mode using the status item

[philipparndt]

Hi,

This PR adds the ability to toggle the table mode from the status item:
fixes #46

I've implemented some more features for the table editor on https://github.com/philipparndt/vscode-text-tables
in case you like to have them I can split them up into different PR's but I don't like to do this work in case you are not interested. The features are:

• EOL character of vscode.TextEditor
• Keep current indentation of the table when formatting
• avoid flicker during forward navigation without change
• Fixed position when using table indent
• Ability to insert a column left to the current position
• Activate on gherkin feature files
• Added command for column deletion